1. Field of the Invention
The present invention relates to a fluorescent ink capable of forming a fluorescent image, and a recording unit, an ink cartridge, an ink-jet recording method, and an ink-jet recording apparatus employing the fluorescent ink.
2. Related Background Art
In ink-jet recording, the ink is ejected by utilizing various methods such as attraction by electrostatic force, mechanical vibration or displacement from a piezo element, pressure caused by bubbles formed by heating the ink, and so forth. In recent years, inks are required to be useful for ink-jet recording in various application fields. In such application fields, various techniques are disclosed not only for forming beautiful color images but also for forming fluorescent images for recording information such as characters, numerals, symbols, and bar codes on a recording medium to record non-visible information (e.g., security information). The fluorescent inks are promising in various application fields, so that development of the fluorescent ink which has high stability, high reliability, and high fluorescence developability is awaited. Inks containing a coloring materials having fluorescence developability (hereinafter, fluorescent coloring materials) disclosed in Japanese Patent Application Laid-Open Nos. 8-151545, 9-132729, 10-193775, 10-298462, and 10-298467; and Japanese Patent No. 233038. Various new recording methods and fluorescent coloring materials are disclosed therein.
The use of a fluorescent coloring material is disclosed, for example, in Japanese Patent Application Laid-Open Nos. 5-293976, 6-191143, 6-322307, 7-009755, 7-305013, 8-053639, 9-003375, 9-01294, 9-137097, 9-137098, 9-137099, 9-165539, 9-241565, 9-255904, 9-286939, 10-007962, 10-183043, 11-080639, 11-320921, and 2000-038529; and Japanese Patent No. 2995853.
The water-soluble fluorescent dye useful as a component of the aqueous fluorescent ink includes C.I.(Color Index No.) Basic Red 1, C.I. Basic Red 2, C.I. Basic Red 9, C.I. Basic Red 12, C.I. Basic Red 13, C.I. Basic Red 14, C.I. Basic Red 17, C.I. Acid Red 51, C.I. Acid Red 52, C.I. Acid Red 92, C.I. Acid Red 94, C.I. Basic Violet 1, C.I. Basic Violet 3, C.I. Basic Violet 7, C.I. Basic Violet 10, and C.I. Basic Violet 14.
Of these dyes, C.I. Acid Red 52, which comes to be excited at an excitation wavelength of about 260 nm to fluoresce at wavelength of 580-640 nm, is especially useful as the coloring material of a fluorescent ink for ink-jet recording, since this dye produces intense fluorescence, having high water-solubility, and causing little problem in safety in comparison with other fluorescent basic dyes.
C.I. Acid Red 52, however, is extremely poor in water resistance. Upon contact with water, the prints recorded with a fluorescent ink-jet recording ink containing such a dye, may lose the characteristic fluorescence, or the printed information may be completely vanished.
The present invention intends to provide a fluorescent ink which is capable of forming a highly fluorescent image with high water resistance of the print, especially a fluorescent ink which is capable of forming a highly fluorescent red image with excellent color tone and high water resistance of the print; and further intends to provide an ink unit, an ink cartridge, an ink-jet recording method, and an ink-jet recording apparatus employing the fluorescent ink. Incidentally, in the present invention, the term xe2x80x9cwater resistancexe2x80x9d signifies not only the capability of retaining the fluorescence of the image but also capability of retaining the visibly recognizable state of the printed information even with loss of the fluorescence.
The above objects can be achieved according to the present invention as below.
According to an aspect of the present invention, an ink-jet recording ink is provided which contains at least a coloring material and an aqueous liquid medium for dissolving the coloring material, wherein the coloring material comprises C.I. Acid Red 52 and at least one direct dye, the content of C.I. Acid Red 52 ranging from 0.1 to 0.4% by weight based on the total amount of the ink, and the content of the direct dye ranging from 0.11 to 0.4% by weight based on the total amount of the ink; and the weight ratio of the direct dye to the C.I. Acid Red 52 being not higher than 1.6.
The preferred embodiments of the present invention include fluorescent inks containing a direct dye having two or more azo groups in the molecule or having a dimer structure; and fluorescent inks containing a direct dye which does not impair the fluorescence of the coexisting C.I. Acid Red 52 and has a color tone, in L*a*b* color space, of a* ranging from xe2x88x9220 to 60, b* ranging from xe2x88x925 to 60, and √{square root over ((a2+b2))} of 30 or more. More specifically, fluorescent inks containing the direct dye in a free acid state represented by the following General Formula(I) 
In General Formula (I), Ar and Ar1 are respectively a substituted or unsubstituted aryl group, and at least one of Ar and Ar1 has a substituent selected from COOH and COSH; J and J1 are respectively a group selected from the following General Formulas (1), (2), and (3) below: 
(In General Formula (1), R5 is independently selected from H, alkyls, substituted alkyls, alkoxys, halogens, CN, ureido, and NHCOR6; R6 being selected from H, alkyls, substituted alkyls, aryls, substituted aryls, aralkyls, and substituted aralkyls. In General Formula (2), T is an alkyl; W is selected from H, CN, CONR10OR11, pyridium, and COOH; (m) is an alkylene chain of 2-8 carbon atoms; R10 and R11 are selected from H, alkyls, and substituted alkyls. In General Formula (3), B is selected from H, and alkyls, and COOH.); and in General Formula (I), R1 R2, R3, and R4 are respectively selected from H, alkyls, and substituted alkyls; L is a divalent organic bonding group; n is an integer of 0 or 1; X is a carbonyl, or one of the following General Formulas (4), (5), and (6) below: 
(In General Formulas (4),(5) and (6), Z is selected from OR7, SR7, and NR8R9; Y is selected from H, Cl, CN, and Z; E is selected from Cl and CN; R7, R8, and R9 are respectively selected from H, alkenyls, substituted alkenyls, alkyls, substituted alkyls, aryls, substituted aryls, aralkyls, and substituted aralkyls; and R8 and R9 may form a five-membered or six-membered ring together with the nitrogen atom bonding therewith.)
When the dye of General Formula (I) does not have an SO3H group, the dye has at least two groups selected from a COOH group and a COSH group. When the dye of General Formula (I) has one or more SO3H groups, the dye has groups selected from a COOH group and a COSH group at least in the same number as the number of SO3H.
The aforementioned fluorescent ink is useful in ink-jet recording.
According to another aspect of the present invention, a recording unit is provided which has an ink container containing the aforementioned fluorescent ink for ink-jet recording, and a head for ejecting the ink.
According to still another aspect of the present invention, an ink cartridge is provided which has an ink container containing the aforementioned fluorescent ink.
According to a further aspect of the present invention, an ink-jet recording method is provided which comprises a step of ejecting the aforementioned fluorescent ink for ink-jet recording by application of energy to the ink.
According to a still further aspect of the present invention, an ink-jet recording apparatus is provided which has an ink container containing the aforementioned fluorescent ink for ink-jet recording, and a recording head for ejecting the ink.